The Pfizer vaccine is 95% effective. Here is how it works

The Pfizer vaccine is 95% effective. Here is how it works

18 December 2020 Off By Oscar Giacomin

The vaccine developed by US company Pfizer and German company BioNTech is 95% effective, even among people who, for their age or for underlying co-morbidities, are at greater risk of getting Covid-19 in a severe form.

Data from phase 3 trials were published on December 10th on the authoritative ‘New England Journal of Medicine’. The journal called the results “a triumph,” while underlying the importance of monitoring patients for a long period in the follow-up. The randomized controlled trial included 43,548 persons, 16 years of age or older. Of these, 21,720 received the vaccine and 21,728 received a placebo. There were 8 confirmed cases of SARS-CoV-2 infection among people who received both doses of the treatment as expected, and 162 cases in the control group who were only administered the placebo. Of the 10 cases of severe Covid-19 among patients participating in the trial, only one had received the treatment.

The authors of the paper explain that the vaccine showed similar efficacy (generally 90 to 100%) across subgroups defined by age, sex, race, ethnicity, baseline body-mass index, and the presence of coexisting conditions. In terms of safety, only minor side-effects were observed: mild to moderate pain at the injection site, fatigue, chills, fever and headache.

The incidence of severe adverse events was low, and similar across the groups who were administered the vaccine and the placebo. However, special caution must be used with patients with “a significant clinical history” of allergies, and the British regulatory agency for drugs (MHRA) advised people in this group not to get vaccinated, at least as long as the cause of the allergic reaction presented by two English health workers who were administered the vaccine is not clear.

The publication of the data had been highly awaited, to give strength to what the pharmaceutical companies had announced, by giving the scientific community the chance to pore over the information. And trial results give hope to Italy as well, as we are waiting for the first vaccine, which has already been approved by regulatory agencies in the UK, Canada and the USA; the European Medicine Agency (EMA) is also expected to approve it with a decision that was supposed to arrive on December 29th, but was moved up by 8 days and is now expected by December 21st. A vaccine that prevents the SARS-CoV-2 virus from causing symptoms in 95 cases out of 100 would definitely mark a turning point, especially in the face of an illness whose outcome is sometimes unpredictable and that can attack several organs. And, as immunologist Eric Rubin and onco-hematologist Dan Longo wrote in the ‘New England Journal of Medicine’ editorial, this vaccine could move from conception to large-scale implementation within a year.

Experts underline that there are questions that are still open: it will be necessary to understand whether vaccinated people can get infected and remain asymptomatic, and it will be crucial to monitor side effects on a longer period. There are also the logistic challenges linked to the fact that the Pfizer/BioNTech vaccine requires storage at -70°C: a factor that “may limit its deployment in some areas,” as the authors of the editorial on the ‘New England Journal of Medicine’ wrote. They added, however, that “the remarkable level of safety and efficacy the vaccine has demonstrated thus far make this a problem that we should welcome solving.”

And the first vaccine to arrive is also the most innovative one, the one using the messenger RNA (mRNA) technology to encode a key protein of SARS-CoV-2, the spike protein, i.e. the wrench that allows the virus to open the Ace 2 receptors, that abound in respiratory tract tissues, and to get inside our cells, where it begins replicating. The same mechanism is used on the vaccine developed by Moderna, which should be greenlighted by the US Food and Drug Administration in a matter of hours. The idea is to push our body to initiate an immune response against the spike protein itself, which is harmless without the rest of the virus: in this way, should the vaccinated person get infected with SARS-CoV-2 afterwards, they would already have the necessary antibodies to recognize the spike protein and get rid of the pathogen.

Thanks to messenger RNA, our body will be able to build an effective defense mechanism before it ever sees the virus. As far as side effects following vaccine administration, the most common are pain and redness at the site of injection. Moreover, about 16% of patients younger than 55 develop a fever, but the temperature goes down again after a couple of days. Generally speaking, the side effects after the first dose are milder, because the immune system is not very active. After the booster dose, which better activates the immune system, typical symptoms of an infection are more common, like fever and fatigue.

What caused the allergic reaction is not yet clear. To be on the safe side, the British regulatory agency advised against vaccinating people who have a recorded episode of systemic anaphylaxis, who are usually allergic to medicines. The USA also recorded a sever allergic reaction after beginning the vaccination campaign: it happened in Alaska, to a health worker who, according to American media, had never presented similar problems in the past. The woman spent one night in the ICU and is currently doing fine, but she will not be administered the second dose of the treatment. On the other hand, it is still too early to know how long the vaccine will remain effective. Another open question is whether the vaccine can protect against viral transmission; on this point, the ‘Wall Street Journal’ wrote that the Moderna vaccine, using the same mRNA technology, seems to block asymptomatic infection as well.

Oscar Giacomin  / General Manager, Facto Edizioni

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